You should eat salmon before a test, berries to prevent Alzheimer's, or a vitamin supplement to increase your memory. You've heard the term "brain foods" since you were a kid, but how much do you really know about them? More importantly, is there really a way to boost your brain power just be eating a certain type of diet? We talked with two experts to unravel the myths and unpack the facts about how much food can really impact your brain.

Just as your stomach, muscles, and heart feed on the nutrients that food supplies, so does the brain. The brain controls almost everything we do and when it takes in chemicals it can have an effect on how it works, both positively and negatively. While you can't push your brain past a certain limit, chances are that your diet isn't providing it with what it needs.

Since the brain is a complicated machine, I talked with Barbara Shukitt-Hale of the USDA Nutrition Research Facility at Tufts University and Gary Wenk, professor of neuroscience, and author of the Your Brain on Food blog at Psychology Today to get a better understanding of how and why certain chemicals in foods have an effect on our brains. Before we delve into the ways you can integrate brain foods into your diet, we have to get an understanding of how those foods get from your mouth to your brain and what they do when they get there.

The Science Behind Why Certain Foods Interact with Your Brain

Studies on the effects of food on the brain are relatively young, and we're still learning why some foods can benefit the brain and why others can't. We do know that certain foods and diets are better for the brain, but figuring out why is still a work in progress. Shukitt-Hale suggests that our bodies may simply absorb the nutrients we take in:

Plants have developed mechanisms to deal with stresses in the environment. Because of sunlight, smog, and temperature they have developed antioxidant or anti inflammatory capabilities. When we ingest them they are protective in our bodies as well.

And Wenk elaborates:

We share an evolutionary history with plants and animals. If the chemicals they consume get into your brain in a high enough concentration it will affect how you think and feel because we share the same chemicals. For example, we hear a lot about the neurotransmitter serotonin in Prozac. Well, lizards have it. Bees have it. In fact if you get a bee sting this summer you've been injected with the bee's serotonin, but you're not going to notice [the effect of serotonin] because the dose is too low. Lots of chemicals out there look a lot like the chemicals in our brain that make us feel good or bad.

Some get across the blood-gut barrier (a lining that keeps certain bacteria and other nasty things out of the bloodstream, but lets other helpful chemicals through) and some don't and we simply excrete them. Then there's some that cross the blood-brain barrier (a layer around your brain that allows some importants things in and keeps others out) but we don't notice them. Let's say you have some sushi and you're consuming that animal's neurotransmitters and it gets into your brain, but you don't notice it. But one of my favorite types of sushi is giant clam, and when you eat that, you're going to have wonderful dreams—it's almost hallucinogenic.

Basically, it's the old saying: you are what you eat. In the case of brain foods, that also includes how much you eat because, as Wenk explains it, it's just a chemical dosage that goes from your mouth to your brain. A lot of foods can interact with the brain, but research suggests that four different types of chemicals and nutrients do so in a positive way. Photo by Scott.

Glucose: The brain draws nearly all its energy from glucose. Like a car in need of gas, if you don't pump it full of fats and sugars (which are converted to glucose) it doesn't run.

Amino Acids: Amino acids come from protein-rich foods and help connect the neurotransmitters which are essential for keeping your brain sharp. These neurotransmitters include: dopamine for proper immune and nervous system function. Norepinephrine for alertness and concentration. Serotonin for mood, sleep, memory, and learning. Acetylcholine for storage and recall of memory.

Antioxidants: Antioxidants like you find in tea or vegetables help regulate the oxidative stress that destroys brain cells. The stress is caused when your body is converting glucose to energy and extra oxygen is created called free radicals. Antioxidants block them so your brain doesn't have to work as hard.

Knowing that, let's look at the actual benefits of brain foods and how you can work them into your diet.

How to Reap the Rewards of Brain Foods

If you're looking for a cognitive boost before a test so you can be smarter for a few hours, you'll be disappointed by the results of most of the research. As it turns out the foods that are good for your brain basically just keep you running. You can overclock your brain with food for a few hours just to get through a rough day, but since most of us don't eat what we're supposed to the real goal is getting our brains up to par. The rewards come in two basic tiers, short term and long term. Shukitt-Hale explains:

We think that there are short-term and long-term benefits. [Brain foods are] doing things like changing gene expression in the brain. Then they have a downstream effect so they protect at a certain point, but that has a cascade effect so you get increases in things like neuronal communication, which means you're making more brain cells. When you make more it will help with your memory.

Just like a good diet makes you feel good in your muscles, a good brain diet does the same for your thinking. In reality, you won't really notice a change unless you're going from a horrible diet to a better one, but that doesn't mean you don't need to try and get the right chemicals and nutrients into the brain as often as possible. Let's look at the big three benefits from eating certain foods and how you can enjoy them. Photo by Pál Berge.

Increase Your Brain's Energy Throughout the Day

Like everything else in your body your brain doesn't work without energy. As far as short-term brain boosts are concerned, this is really the only way to get your brain in tip-top shape right away. It's not hard to do because the brain's primary energy source is glucose and we get glucose from nearly everything we eat. While candy can give you a quick high, it's better to fuel your brain with foods that slowly release carbohydrates (which are then converted to glucose). Here's a couple suggestions on how to regulate glucose for optimal thinking.

Graze slowly throughout the day to regulate glucose levels: It turns out that too much of a good thing is just as bad as under doing it. The brain operates best with about 25 grams of glucose in the blood stream, which is about what you'll find in a banana. Beans, lentils, whole grain pastas, and split peas are all good foods to casually snack on to keep your brain charged with glucose and optimized for thinking.

Lower your overall glycemic index: Not everyone has the luxury of grazing casually on food all day long, but you still want to moderate your glucose level. You can do so by lowering your glycemic index. The glycemic index is a number that shows how foods affect glucose level in your bloodstream. Foods with a low glycemic index release glucose slowly into the bloodstream so as not to overwhelm your brain. The problem is that a lot of these foods interact with each other so it's difficult to pinpoint what exactly works and what doesn't. For instance, if you eat protein with some whole wheat bread the glucose is released gradually over time, but if you eat bread by itself it causes a slight spike in glucose level then drops quickly. The Franklin Institute has a breakdown of the glucose levels in a number of foods to help you plan out meals.

Get energized on amino acids: Two amino acids, tryptophan and tyrosine, can get through the blood-brain barrier. Tryptophan, as we all know from Thanksgiving, has a calming effect (which is often exagerated as a sleep-inducing effect). Tyrosine makes you feel energized. When the body breaks down protein it creates amino acids to help itself (and the brain) function. Fish, meat, eggs, cheese and yogurt are all great sources of this and working in one of these elements into each meal is a good way to ensure your brain gets what it needs.

Keeping your brain running every day is just the first part. The second and perhaps most interesting is food's ability to repair the damage you've already done. Photo by Ernst Vikne.

Replace Lost Brain Cells

If you had to take a drug and alcohol class in school then you likely heard that brain cells are irreplaceable. It turns out that's not entirely true. While we're not going to tell you to go out and get wasted to test the theory, research from MIT, Princeton, and others suggests that we continue to make new brain cells throughout our lives. Brain cells affect the speed of your brain and increase your working memory, which in turn makes you a better learner.

According to Shukitt-Hale, certain foods can change gene expression in the brain and increase neuronal brain communication by creating new brain cells. It's thought that one food type that may help brain cell production comes from the fatty acid omega-3 which is found abundantly in fish and walnuts. Eating a serving of these every day in combination with exercise can help rebuild those brain cells.

Protect Against Cognitive Decline

It's no secret that as you age you have problems with memory and cognition. However, you can help your brain out a little by creating a protective barrier and keeping it clean and free of harmful free radicals. Free radicals are caused when an imbalance of oxygen creates oxidative stress. When this happens the brain is forced to work overtime to keep them under control. Antioxidants can do the work so the brain doesn't have to. You can also work in a few different foods that help strengthen the brain in the long term to help stave off the inevitable decline. The benefit is that many of these effects may cascade down and offer a few short-term benefits as well.

Eat your antioxidants daily: Antioxidants fight off the free radicals that like to destroy brain cells and when they do that your brain is kept in good running shape. Shukitt-Hale's studies on berries (which are high in antioxidants) have shown that antioxidants may also prevent the inflammation in the brain that leads to neuronal damage. This suggests that berries might help your brain work better for a longer period of time. How much do you need? A cup a day should do the trick. Other good antioxidants include spinach, broccoli, carrots, and a wide variety of teas.

Is there a proven way to prevent cognitive decline? Wenk suggests a completely different approach for getting the same long-term cognitive benefits: eat less. He explains:

We operate at an evolutionary timed balance and more often than not we tend to imbalance our brain function with chemicals. About ten or fifteen years ago we gave up on cognitive enhancement because we figured out that we're about as smart as we can stand and we all function about as fast as possible in our brains.

We can push ourselves a little bit, but does it raise your IQ? No. Thus far, the only thing we've ever discovered that really slows down the decline is dietary restriction. It's not a huge change, it's cutting out 30% of your calories. It's the only thing that's been proven to help you live longer, be smarter, and stave off disease.

The research on food's direct relation to your brain is still young and while researchers have an idea of what works, they're still still learning why and how. The idea of a brain food isn't so much about pushing your brain past its limit. Rather, it's about protecting and utilizing the brain's already immense power. The USDA's Food Plate has suggestions built in to help the brain, but knowing why and how these work might make that choice to include spinich with your next meal a little easier. Will you suddenly get smarter? Nope, but at least you'll be operating at your full potential for a longer period of time. Have some tips for working these foods into your diet? Share them in the comments.